Leadless Pacemaker Implantation in Fontan Patients with Multimodality Imaging: Tips and Tricks

Current leadless pacemaker (LP) systems, which have been developed and used in patients with normal cardiac anatomy, are rare and technically even more challenging to implant in patients with congenital heart diseases, especially with univentricular physiology and Fontan palliation. We report two cases of percutaneous LP implantation in an adult and a child, respectively, highlighting the unconventional approaches, different challenges, and use of multimodality imaging in patients who underwent a Fontan operation.


Introduction
Transcatheterdelivered, fully encapsulated active fixation based leadless pacemaker (LP) systems offer an excellent alternative for endocardial/epicardial approaches to address pacing needs in patients with structurally normal hearts. 1 Patients with congenital heart disease are a unique group of patients with additional considerations second ary to a lack of venous access to cardiac chambers, com plex intracardiac anatomy, higher risk of thromboembolic events, infection, and the need for atrioventricular (AV) synchrony.3][4][5] The Micra™ transcatheter pacing system (TPS) (Medtronic, Minneapolis, MN, USA) is typically implanted in the catheterization laboratory under fluoroscopic guidance.The device is mounted on its own dedicated 27French (Fr) introducer sheath and advanced to the right ventricle (RV) percutaneously through the femoral vein with the aim of a septal position with fixation achieved by deployment of two of four niti nol tines.We report two cases of percutaneous LP implan tation, in an adult (case 1) and a child (case 2), highlighting the unconventional approaches and different challenges in patients who underwent a Fontan operation (Figure 1).Both patients had complete heart block with preexisting epicardial pacemaker system implants and pacemaker dependence.Case 1 was a patient who had a double inlet left ventricle (DILV), status post-lateral tunnel type of Fontan palliative surgery, thus excluding direct access to cardiac chambers via the superior vena cava (SVC) and inferior vena cava (IVC).Case 2 was a 38kg child who had tricuspid atresia and hypoplastic RV with heterotaxy syndrome (left atrial isomerism, interrupted IVC with azygous continuation).He was status post-extracardiac fenestrated Fontan procedure with a Kawashima oper ation, bilateral bidirectional Glenn anastomosis, and The Journal of Innovations in Cardiac Rhythm Management, August 2024 creation of the right pulmonary artery (RPA) to right atrium fenestration and hepatic veins to the RPA conduit.Thus, direct access to cardiac chambers was absent, mak ing approaches to Micra™ implantation challenging and nontraditional.

Case 1
A 32yearold woman with univentricular physiology, DILV, and status post-lateral tunnel Fontan (Figures 1  and 2), with complete AV block, presented with recur rent epicardial system infections caused by Enterobacter cloacae and pacemaker pocket dehiscence.She had mul tiple pocket revisions, prolonged antibiotic therapy, and wound vacuum application to abdominal sites.After dis cussing the possible options and associated procedural risks (redo sternotomy, revision of leads and pocket), we decided to proceed with LP implantation.Due to her uni ventricular physiology, a Micra™ AV (Model MC1VR01; Medtronic, Inc., Minneapolis, MN, USA) leadless system was chosen for implantation.This device offers detection of atrial contractions using the device's builtin threeaxis accelerometer to provide AV synchronous (VDD) pacing. 6

Implantation technique
After the patient was placed under general endotracheal anesthesia and given intravenous antibiotics, an 8Fr sheath was placed in the right femoral vein and a 10Fr sheath was placed in the left femoral vein.An intracar diac echocardiography (ICE) catheter (ViewFlex™ Xtra ICE Catheter; Abbott, Chicago, IL, USA) was also inserted   apex, and several tug tests under fluoroscopy showed stable pacemaker positioning.The pacing and sensing parameters were adequate.The TEE confirmed that there was no entrapment of the valvular apparatus, and there was also no newonset AV valve or neoaortic regurgita tion.After removal of the Micra™ delivery catheter, there was significant righttoleft shunting with desaturation into the 70s.Using TEE evaluation, the Fontan fenestra tion was closed using a 20mm GORE ® Cardioform Septal Occluder (Figure 6).On followup, both the Micra™ TPS and GORE ® Cardioform Septal Occluder remained in a

Case 2
A 15yearold boy, weighing 38 kg, with univentricular physiology including tricuspid atresia and hypoplastic RV (Figure 1) with heterotaxy syndrome, left atrial isom erism, interrupted IVC, and bilateral SVCs presented with chest discomfort and chronic epicardial ventricular lead dysfunction with a high pacing threshold as well as intermittent loss of pacing capture and a pacemaker gen erator nearing depletion.He was status post-extracardiac fenestrated Fontan procedure with Kawashima oper ation, bilateral bidirectional Glenn anastomosis, and the creation of the RPA to right atrium fenestration and hepatic veins to the RPA conduit.Thus, direct access to cardiac chambers via the right and left SVCs, interrupted IVC, and hepatic veins was absent, making approaches to Micra™ implantation challenging and nontraditional.He had complete AV block with pacemaker dependence.Just 3 years before this presentation, he had undergone repeat sternotomy for the addition of a ventricular pacing lead due to lead failure and pacemaker generator replace ment operation.That operation was difficult and compli cated with prolonged, extensive surgical dissection for ventricular surface exposure.The lead body could not be directly secured to the ventricular surface and was stabi lized using sutures to the shaft of the lead.He also had significant postoperative bleeding or chest tube drain age requiring a blood transfusion.After discussing the possible options and associated procedural risks (redo sternotomy, revision of leads and pocket, replacement of generator), we decided to proceed with percutaneous LP (Micra™ AV) implantation via a right internal jugular venous (RIJ) approach.

Implantation technique
The procedure was performed under general endotra cheal anesthesia.After positioning and draping the right side of the neck, percutaneous vascular access was obtained in the RIJ vein, and an 8Fr sheath was placed.Heparin was administered, and the activated clotting time was monitored throughout the procedure.
A pigtail catheter was advanced, and angiograms were performed in the Fontan baffle to delineate anatomy and landmarks for transbaffle access via existing fenes tration known by echocardiogram and prior angiogram ( Figure 7).There was a small fenestration with flow of contrast noted into the cardiac chamber at the inferiorleft part of the Fontan baffle.The pacing and sensing parameters were excellent.The TEE confirmed that there was no entrapment of the val vular apparatus, and there was also no newonset mitral valve or neoaortic regurgitation.After a brief discussion with the surgery and cardiac team, it was decided not to close the fenestration that was dilated at this juncture.The tether was cut and removed, which was followed

Tips and Tricks for LP Implantation in Fontan Patients with Multimodality Imaging
The Journal of Innovations in Cardiac Rhythm Management, August 2024 by the removal of the delivery catheter and sheath.The device remained in a stable position.The patient toler ated the procedure well and was extubated in the cathe terization lab.
Both patients were discharged from hospital and have been followed up with (case 1 for 5 months; case 2 for 1 month) in the outpatient setting without any thrombo embolic complications or new concerns, and both reported a return to baseline activity of daily living.

Discussion
Our report describes successful implantation of leadless Micra™ pacemakers with innovative approaches in chal lenging postoperative anatomy of two Fontan patients with complete heart block and highrisk limited alter natives.In case 1, a Micra™ AV TPS was successfully implanted via an IVC approach and a transFontan baffle puncture in a patient with complex congenital heart dis ease, DILV, and lateral tunnel Fontan palliation.In case 2, a child weighing 38 kg with univentricular physiology involving tricuspid atresia with heterotaxy syndrome, left atrial isomerism, interrupted IVC, and bilateral SVCs, a Micra™ AV was implanted with an RIJ approach.This patient had a fenestrated Fontan procedure with a Kawashima operation, bilateral bidirectional Glenn anas tomosis, and creation of the RPA to the right atrium fenes tration and hepatic veins to the RPA conduit.In addition, a previous fenestration at a more favorable location was already closed by a septal occluder device.Thus, an RIJ venous approach with a transFontan baffle access via an existing inferior fenestration was planned.In both cases, for Micra™ implantations, we used a 65cmlong 26Fr GORE ® DrySeal Flex Sheath with a hydrophilic coating that offers enhanced flexibility and kink resistance to cross the baffle instead of the 55cmlong, 27Fr Micra™ introducer sheath, which is prone to kinking.The use of the DrySeal sheath also allowed us to keep a wire in position outside of the Micra™ delivery catheter, and this wire was used to guide the delivery sheath for fenestra tion device closure in case 1 after Micra™ implantation, rather than recrossing the baffle.In case 2, due to the short length of the delivery sheath inside the body from the RIJ approach and a complex wire loop formation, it was helpful to perform balloon angioplasty over the stiff Amplatz wire at the fenestration and maintain the wire across the fenestration during Micra™ delivery.
In patients with various types of Fontan operations, post operative anatomy can vary with areas of contiguity with the native atrium and discontinuous areas between the Fontan baffle and native atrium along its length.Thus, it is critically important to perform a transbaffle punc ture at a site of continuity prior to dilation of the punc ture site.In case 1, the EAM system-guided voltage map ping, vector propagation, image integration, depiction of the chamber ultrasonic contour, and visualization of the sheath in conjunction with ICE helped identify the site of the transbaffle puncture and reduce radiation exposure during the procedure.However, use of such a mapping system is not mandatory for all Fontan cases, especially those with preexisting fenestration as demonstrated by the use of fluoroscopy and TEE only in case 2. Imaging guidance with TEE and/or ICE is crucial during trans baffle puncture and manipulation of the Micra™ delivery catheter through the fenestration and AV valve into the ventricular site without injury or impingement of the val vular apparatus.
LP systems, especially those that offer AV synchrony, are an attractive alternative to epicardial systems for the complex congenital heart disease population.The prev alence of LPrelated infections is low due to the absence of a subdermal surgical pocket and pacemaker leads.
3][4][5] The mechanical atrial sensing algorithm produced 60%-64% AV synchrony on followup 2-4 weeks later.Further programming assess ment and adjustments were made at followup visits to optimize and increase AV synchrony.
Fontan palliation, which routes systemic venous blood directly to the pulmonary vascular bed with the lack of a subpulmonic pump, leads to significant circulatory challenges and complications due to chronic low car diac output, high central venous pressure, and venous stasis.Thrombus formation and the risk of thromboem bolic events are increased due to various factors, such as lowvelocity nonlaminar flow, prosthetic material, endothelial dysfunction, blindending pouches, atrial arrhythmias, and altered procoagulant and anticoagulant factors. 7,8Consequently, many, if not all, patients with a Fontan need antithrombotic prophylaxis, although reg imens vary.The adult in case 1 was already on a non vitamin K antagonist oral anticoagulant (NOAC) that was continued, and case 2 was started on a NOAC after Micra™ implantation.The child in case 2 was on aspirin only prior to the Micra™ implantation procedure.More cases and longer followup data are needed for an ideal anticoagulation strategy for an LP indwelling in a sys temic ventricle.

Conclusion
Transcatheter LP implantation in complex congenital heart disease can be aided by multimodality imaging as well as innovations in standard equipment and tech niques during the implantation procedure.

Figure 2 :Figure 1 :
Figure 2: An angiogram (case 1) in the inferior vena cava demonstrates the typical appearance of a lateral tunnel Fontan without any fenestration and connections of the inferior and superior vena cavae with the pulmonary arteries.

Figure 3 :
Figure3: Electroanatomic and voltage mapping with activation vectors displays electrical activation of the Fontan chamber originating at the inferomedial aspect signifying anatomic and electrical contiguity in the region between the common atrium and surgically fashioned lateral tunnel/Fontan (case 1).This area was chosen as the site of puncture to enter the common atrium.

Figure 4 :
Figure 4: A 26-Fr DrySeal sheath and dilator assembly is advanced after transbaffle puncture into the common atrium with the wire tip in the DILV (case 1).
Tips and Tricks for LP Implantation in Fontan Patients with Multimodality ImagingThe Journal of Innovations in Cardiac Rhythm Management, August 2024 stable position with adequate pacing function character istics.The patient underwent an uneventful removal of the infected epicardial pacemaker system.

Figure 5 :
Figure 5: A fluoroscopy image showing the 26-Fr DrySeal sheath withdrawn into the Fontan and the Micra™ delivery catheter and the LP advanced into the DILV (case 1).A separate 0.035-in wire is noted in the LUPV advanced outside the Micra™ delivery catheter across the same puncture site through the DrySeal sheath.

Figure 6 :
Figure 6: A cineangiogram view demonstrating a 20-mm GORE ® Cardioform Septal Occluder deployed at the site of puncture without any contrast flow in the common atrium (case 1).Also seen is the Micra™ leadless pacemaker in the double inlet left ventricle.
TransFontan baffle access was obtained by crossing with a 0.035in GLIDEWIRE ® guide wire (Terumo Medical Corp., Somerset, NJ, USA) and a 4Fr angled GLIDECATH ® catheter (Terumo Medical Corp., Somerset, NJ, USA) from the inferior fenestration.The wire and the catheter were advanced into the LV/ single ventricle and across the aortic valve into the right innominate artery, but the Amplatz™ Super Stiff 0.035in wire could not be exchanged and advanced due to the formation of a large loop in the atrium.The guidewire was then crossed back into the Fontan baffle from the left atrium (LA) via the superior fenestration into the RPA, creating a loop of SVC → Fontan → inferior fenestration → LA → superior fenestration → Fontan baffle.This loop was preserved by exchanging with an Amplatz™ Super Stiff wire and was used for the rest of the procedure.Angioplasty of the inferior fenestration was performed over this wire with a 10mm OPTA ® PRO balloon (Cordis, Santa Clara, CA, USA) to facilitate advancement of the 26Fr DrySeal sheath ( Figure8).The RIJ access site was dilated with a Coons taper dilator (Cook Medical, Bloom ington, IN, USA), and a 26Fr, 65cm GORE ® DrySeal Flex Introducer Sheath was introduced over the Amplatz™ wire for the delivery of the Micra™ device instead of the provided 27Fr Micra™ introducer sheath.The Micra™ delivery catheter system was prepped and inserted into the DrySeal sheath by the side of the Amplatz wire and advanced to the apex of the LV under fluoroscopic and TEE guidance with gentle navigation (Figure9).Continu ous assessment by TEE was performed to ensure crossing across the mitral valve without any entrapment or injury to the AV valve or other cardiac structures.The position ing and site selection of the implant were guided by mul tiple fluoroscopic views, small contrast injections, and TEE evaluation prior to applying pressure and deploy ment of the Micra™ device using the standard technique.

Figure 7 :
Figure 7: An angiogram (case 2) with a pigtail catheter in a Fontan baffle from a right internal jugular venous approach demonstrates a small fenestration inferiorly and leftward.A more superior fenestration site is noted with a septal occluder device in situ.Figure 8: A fluoroscopic view (case 2) demonstrating the complex loop (right internal jugular vein → superior vena cava → Fontan → inferior fenestration → left atrium → superior fenestration → Fontan baffle) with a stiff 0.035-in Amplatz™ wire and balloon inflation at the inferior fenestration site.

Figure 8 :
Figure 7: An angiogram (case 2) with a pigtail catheter in a Fontan baffle from a right internal jugular venous approach demonstrates a small fenestration inferiorly and leftward.A more superior fenestration site is noted with a septal occluder device in situ.Figure 8: A fluoroscopic view (case 2) demonstrating the complex loop (right internal jugular vein → superior vena cava → Fontan → inferior fenestration → left atrium → superior fenestration → Fontan baffle) with a stiff 0.035-in Amplatz™ wire and balloon inflation at the inferior fenestration site.

Figure 9 :
Figure 9: A fluoroscopic image (case 2) showing the Micra™ device advanced inside a GORE ® DrySeal Flex Introducer Sheath alongside the Amplatz™ wire, which is maintained across the fenestration in a complex loop (from right internal jugular vein → superior vena cava → Fontan → inferior fenestration → left atrium → superior fenestration → Fontan baffle).